1. Technical Field
The present disclosure relates to a file generating method and file generating apparatus that generate MP4 files.
2. Description of the Related Art
A file format used for conventional optical discs is an MPEG2-TS (MPEG-2 Transport Stream) scheme prescribed by ISO/IEC 138181-1. Hereinafter, the MPEG2-TS scheme is just referred to as MPEG2-TS. That is, a file made through multiplexing of a video stream, voice stream, and subtitle stream in an MPEG2-TS file format is recorded in an optical disc. Specifically, according to MPEG2-TS, streams such as a video stream, voice stream, and subtitle stream are each divided into a plurality of 188-byte TS packets, multiplexed, and recorded in an optical disc. This MPEG2-TS is optimized for broadcast or a medium like an optical disc that transmits or records data that is read and processed sequentially from top. Therefore, even a consumer electronic product with relatively small buffer capacity can read, decrypt, and play the stream efficiently.
In contrast, the file format currently used in content delivery over a network these days is the MP4 scheme prescribed by ISO/IEC 14496-12. Hereinafter, the MP4 scheme is just referred to as MP4. MP4 adopts extremely flexible data structure on an assumption of application of MP4 to a medium that allows random access, such as a HDD (Hard Disk Drive) and a flash memory. In a general usage pattern of this MP4, a stream such as a video stream, voice stream, and subtitle stream is divided into several-second units called fragment, and these fragments are arranged sequentially to constitute one file.
An optical disc is expected to be still utilized often as a medium for distributing quality content, such as 4K, that is expected to be widely used in the future, due to a problem of a price per bit. In contrast, a smart phone or tablet, which fails to have an optical disc drive, is used as a terminal for receiving and playing content distribution over a network, through utilization of high portability or recent large screen and high resolution. For this reason, a smart phone or tablet has a lot of functions and processing that conform to MP4, and application of MPEG2-TS shows little progress.
Therefore, when content that is an MPEG2-TS file distributed with an optical disc is copied to the smart phone or tablet, the file format of the content may be converted into MP4 (for example, refer to Patent Literature 1). An MP4 file, which is a file of MP4, is generated by such conversion.